First X-ray source in Andromeda

The first X-ray source in Andromeda is an astronomical X-ray source probably detected between June 12, 1962, Scorpius X-1, and January 9, 1979, Sagitta X-1 (Sge X-1), though it may not have received the X-1 designation.
Andromeda as a constellation
The celestial sphere is divided into 89 areas. These are the International Astronomical Union (IAU) 88 modern constellations of astronomy. Although there are only 88 IAU constellations, the sky is actually divided into 89 irregularly shaped boxes as the constellation Serpens is split into two separate sections, Serpens Caput (the snake's head) to the west and Serpens Cauda (the snake's tail) to the east. From each of these areas of the celestial sphere, incoming X-rays (X-radiation) have been detected above the Earth's atmosphere, as X-rays do not penetrate.
Andromeda is in the northern sky. Of all the constellations it is 19th in celestial area at 722 sq. deg. A relatively uniform distribution of 1,000 astronomical X-ray sources would yield at least seventeen. Or, by 1984 and the HEAO 1 A-1 catalog, (840 X-ray sources known), there might have been at least fifteen X-ray sources detected in Andromeda.
Searching early catalogs
In 'A Catalogue of Discrete Celestial X-ray Sources', which contains 59 astronomical X-ray sources detected by sounding rockets and balloons, there is no source in Andromeda.
The Vela series of satellites generated detection of some 25 gamma-ray bursts (GRBs) included in 'A Preliminary Catalog of Transient Cosmic Gamma-Ray Sources Observed by the VELA Satellites', This catalog contains no source in Andromeda.
The early Uhuru catalog contains three astronomical X-ray sources within the constellation Andromeda that were detected early: 2U 0022+42, 2U 0033+24, and 2U 0043+32. Each of these is confirmed later: 2U 0022+42 at 3U 0021+42, 2U 0033+24 at 3U 0032+24, and 2U 0043+32 at 3U 0042+32. The two preliminary reports (1 ASE and 2 ASE) contain some 132 apparent sources, whereas the 2U catalog contains 125 superseding sources. So, it is unlikely that M31 is Andromeda X-1.
==2U 0022+42==
The earliest apparent detection of X-rays from Andromeda occurred in 1971 at equatorial coordinates right ascension (RA) declination (Dec) , 2U 0022+42, and is claimed from M31. at 4U 0037+39 is in M31. 4U 0037+39 is ~4.8° from 2U 0022+42. The error box for 2U 0022+42 has the corners: RA Dec , RA Dec , RA Dec , and RA Dec . 4U 0037+39 is not listed in earlier catalogs and its error box may just overlap a portion of that for 3U 0021+42 for an error box of ~2° x 7.5°, with the long axis radial toward 4U 0037+39.
==2U 0033+24==
The error box for 2U 0033+24 has corners at J1950 RA Dec , RA Dec , RA Dec , and RA Dec .
2U 0033+24 is further confirmed at 4U 0028+22.
2U 0043+32 is a high galactic latitude, soft X-ray transient (SXT). Four distinct outbursts occurred in February 1977 whose interval is estimated at 11.6 d which results in it being classified as a high galactic latitude X-ray transient. 2U 0043+32 is a low-mass X-ray binary (LMXB). 3U 0042+32 is assigned an error of 0.140 sq. degrees.<ref name=Murray/>
Visibly dark X-ray source
Of the first X-ray sources discovered in each constellation (126 for 89 areas), some 63% are visibly dark. These visually dark X-ray sources can be radiative cosmic dust, hydrogen gas such as an H II region (e.g. the Orion Nebula), an H I region of hydrogen, a molecular cloud, or a coronal cloud.
Both 2U 0022+42 and 2U 0033+24 are probably visibly dark X-ray sources.

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